The Theory of Plate Tectonics

Tectonic Plates

• Tectonic Plates are pieces of lithosphere that move around on the Athenosphere.

• Plates range in size.• Some plates contain

both continental and oceanic crust.

• Plates link like a puzzle.

Tectonic Plate Boundaries

• A Plate Boundary is the place where two plates meet.

• There are 3 types of boundaries.

1. Convergent

2. Divergent

3. Transform

Convergent Plate Boundaries

• At Convergent boundaries two plates collide.

• Three results may happen from the collision.

• The type of plates that collide will determine one of three geographic features.

Convergent Plate Boundaries

1) If two continental plates collide, a high mountain range may form.

2) The mountain may take many of years to form.

Convergent Plate Boundaries

3) When a plate of oceanic lithosphere collides with a plate of continental lithosphere, the denser oceanic lithosphere sinks, or subducts beneath the less dense continental crust.

4) This process is called subduction.5) Subduction may cause a chain of volcanoes to form parallel

to the fault.

5) When two oceanic plates collide, the denser of the two will submerge.

• A series of volcanic islands called island arc may form parallel to the fault.

Divergent Plate Boundaries• Where two tectonic

plates separate.• Some appear on

land.• Most appear on sea

floor.• As plates spread,

magma rises to the ocean floor.

• The magma cools and forms new lithosphere.

Transform Plate Boundaries

• Two tectonic plates slide past each other.• Most transform boundaries occur in the sea floor at

mid-ocean ridges.• San Andreas Fault in California occurs both on land

and in the ocean.

San Andreas Fault

Causes of Tectonic Plate Motion• Heat is transferred

from the Earth’s core through convection.

• When rock is heated, it becomes less dense and moves towards the surface. At the surface, cooler dense rock tends to sink thru subduction.

• Convection currents are formed all over the mantle, causing plates to move.

Tracking Tectonic Plate Motion

• Plates move so slow that they are measured in centimeters per year.

• Scientists use GPS and satellites to measure exact distances.

• Scientists use sea floor spreading to measure ocean plates.